Cloth media filtration devices are well known in the industry. Such devices employ cloth filter media stretched over large drums, plates, plenums or multiple disk-type frames. An example of a preferred disk-type filtration device is known as the AquaDisk® cloth media filter, a product of Aqua-Aerobic Systems, Inc., the assignee of the present invention. Other examples may be found in U.S. Pat. Nos. 4,090,965 and 4,639,315.
The “cloth filter media” typically used in such devices include textile cloth membranes of a cellulose base material, other natural or synthetic fibers woven, knitted or wrapped into a tight, single layer or multiple layer fabric or matting to obtain the desired thickness or porosity. Such fibers may be needle felted to a textile support fabric for strength. The fibers may also be woven into a dense cut pile fabric supported by an open weave textile support grid. For ease of reference, the present inventions will be described and claimed in relation to a cloth filter media having a support fabric and a pile made of pile threads attached to said support fabric. It will be understood that the inventions are not so limited.
The cloth filter media is placed in the flow path of the fluid stream containing the solid particles which are to be removed by the filtering process of the cloth media filtration device. The particles larger than the openings of the cloth filter media are retained on the upstream, or influent side, of the cloth filter media while the remaining flow or effluent passes through the cloth filter media. The effective surface area of the cloth filter media dictates the capacity of the filtration operation, i.e., that amount of cloth that is capable of conducting the filtration operation. Over time, the solids build up on the influent side of the cloth filter media and impede the rate of filtration. This creates a hydraulic resistance which necessitates the cleaning of the influent side of the cloth filter media, which is commonly done by backwashing using suction.
Periodic backwashing is conducted using a backwash assembly. The typical backwash assembly includes a backwash shoe which is located adjacent to the influent side of the cloth filter media and which is sealed to and in fluid communication with a suction chamber. Backwash shoes typically include one or more face plates and a suction slot. The suction chamber is connected to a suction pump by a hose or pipe which actuates the reverse flow of liquid through the suction slot of the backwash shoe from the effluent side of the cloth filter media to the influent side of the cloth filter media.
During the backwashing operation, the cloth filter media may move relative to the backwash assembly or the backwash assembly may move relative to the cloth filter media, depending upon which type of cloth media filtration device is used. Due to the suction and the relative motion between the cloth filter media and the backwash shoe, the suction pressure draws the effluent across some or all of the piles of the cloth filter media into the suction slot to dislodge the accumulated solids from the influent side of the cloth filter media. The combination of reverse filtration flow and the flexing of the piles into and across the suction slot work to dislodge the accumulated solids from the cloth filter media.
There are a variety of known backwash shoes as part of backwash assemblies that are used to backwash cloth filter media. Examples of backwash shoes and methods of using them may be found in U.S. Pat. No. 6,103,132. In that example, the leading edge of the backwash shoe (i.e., the portion of the backwash shoe that is in the direction of motion of the backwash assembly or the portion of the backwash shoe that is in the direction of the moving cloth) compresses the pile threads to the support fabric just prior to the suction slot. Upon reaching the suction slot, the pile threads are abruptly released into the suction slot and cleaned. Thereafter, the trailing edge of the backwash shoe compresses the pile fibers toward the support fabric. Filtration may then be resumed as the relative motion between the cloth and the trailing edge of the backwash shoe exposes the influent side of the cloth media to the fluid stream.
Other types and configurations of backwash shoes are also known, including those that do not contact the cloth (or at least the support surface of the fabric) and those with a series of perforations and other variations. See, for example, U.S. Pat. Nos. 7,678,284; 8,048,296; 9,352,255; 8,852,445; and 6,294,098. In these types of backwash shoes, the pile threads of the cloth filter media may not be compressed by the backwash shoe against the support fabric. Instead, the piles remain in a generally extended or partially extended position upon completion of backwashing.
As will be appreciated by those of skill in the art, the effective surface area of the cloth filter media is a key parameter in the sizing, performance and capacity of the cloth filter media filtration devices. Therefore, there is a need to increase the effective surface area of the cloth filter media without the need to use larger equipment, more media, the use of more filtration devices or extensive modification of such units.
While the above referenced and other known backwash shoes provided varying levels of effectiveness in cleaning, there is a need to increase the efficiency of the overall backwash operation in both new and existing filtration facilities. As importantly, there is a need to improve the backwash operation such that the surface area of the cloth filter media is increased to more efficiently and effectively resume the filtration operation after backwashing.